The present invention relates to solenoid valves and more particularly, to a solenoid valve that exhibits a dynamic force field distribution with effectively eliminated negative flow forces, suitable for use in vehicular anti-lock braking systems.
Numerous varieties of solenoid valves are conventionally available, many of which are constructed for use in specific applications. Two-way solenoid valves are widely used and are generally provided in either a normally closed or a normally open configuration. Such valves are conventionally used in anti-lock braking and related systems wherein two solenoid valves per wheel or more specifically, two solenoid valves per ABS control channel are typically used. The valve pairs are usually arranged as one normally open and one normally closed. The normally open valve typically resides between the wheel brake and the master cylinder and the normally closed valve generally resides between the wheel brake and the recirculation pump inlet.
Such a paired solenoid valve arrangement provides control of the wheel brake for pressure modulation purposes. Typically, the wheel brake pressure may be independently reduced, held at an intermediate pressure, or reapplied up to the master cylinder pressure. In order to control the rate at which the pressure builds or decays in the wheel brake, the solenoid valves are typically pulsed open and closed in a very rapid fashion in order to effectively control the flow rate of fluid either to or from the wheel brake.
To effectively control flow rates in a precise manner, solenoid valves used in braking systems respond quickly to control signals. Typical solenoid valves can fully open or fully close in milliseconds. An aspect of this fast response characteristic is that it results in the rapid acceleration and deceleration of the high velocity fluid flowing through the small ports in the valves.
It has been discovered as part of the present invention that, particularly with the normally open solenoid valve, this phenomenon causes a localized pressure pulse within the valve which subsequently travels down the entire column of hydraulic fluid that connects the solenoid valve in the ABS modulator to the master cylinder. Upon reaching the master cylinder, this pressure pulse can excite audible noise and vibrations. Although these results do not effect the operational characteristics of the braking system they may be perceivable and therefore, are generally considered as undesirable.